S numbers were eliminated in the 2009 addenda. Most materials formerly assigned S numbers are now assigned P numbers, most, because in a few cases, former S number materials were deleted.
In some cases former S number materials were assigned a different P number. If you have an existing procedure qualified using Sx which is now Sy, you can still use these procedures within certain limitations. It's important to note that materials must have a specified minimum tensile strength to be used for procedure qualification. I highly recommend you spring for a current edition of Sec IX and carefully review QW 420.